<p>One asterisk: *</p>
<p>One underscore: _</p>
<p>Two asterisks: **</p>
<p>With spaces: * *</p>
<p>Two underscores __</p>
<p>with spaces: _ _</p>
<p>three asterisks: ***</p>
<p>with spaces: * * *</p>
<p>three underscores: ___</p>
<p>with spaces: _ _ _</p>
<p>One char: <em>a</em></p>